Telephone system



May 19, 1936. R. l.. sToKELY 2,041,096

TELEPHONE SYSTEM Filed De@ 2S, 1954 2 sheets-sheet 1 A T TORNEV May 19, 1936.` R STOKELY l ZWL TELEPHONE SYSTEM v 2 Sheets-Sheet v2 Filed Dec. 28, 1954 /lV VEN TOR R. yL. s Tom-y Patented May 19, 1936 PATENT OFFICE TELEPHONE SYSTEM y Ray L. Stokely, Floral Park, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 28, 1934, Serial No. 759,441

6 Claims.

This invention relates to telephone systems andV the branch exchange vand arranged to transfer a call to the attendant in case the connection is extended in the central oiice to a trunk employed in completing toll calls. The control means comprises a three-element gas-filled tube having its control element connected to one of the conductors of thetrunk and its anode element connected tothe Winding of a transfer relay, On calls other than toll calls, the potential impressed upon the control element of the tube is insufficient to cause its operation but on toll calls the tube responds to a momentary connection of a high potential v to effect the transfer of the call to the attendant. A feature of the invention is a toll trunk and associated control apparatus so arranged that a high potential battery is normally connected to one of the conductors of the trunk to indicate that it is a toll trunk, the high potential battery being disconnected immediately after seizure of the trunk.

One system arranged in accordance with this invention is represented schematically in the drawing which forms a part of this specification. The invention is not, however, limited in its applicationto this particular system but may be applied to all automatic and semi-automatic sys- Y tems in which the service to which some of the 4o subscribers are entitled is restricted in some manner, such for instance as being restricted to local service.

Referring to the drawings:-

Fig. 1 represents a private branch exchange BO and Fig. 2 represents a central office CO.

In Fig. l, A and B represent stations in the private branch exchange, LFI represents a linender switch, SC represents a selector-connector switch, TI represents apparatus associated with an outgoing trunk 50 which connects the branch office BO with the central office CO, T2 represents apparatus associated with a local trunk 4|] leading to an attendants position, and CDI represents a cord at the attendants position.

In Fig. 2, C and D represent stations in the main office, LF2 represents a line-finder switch, SI represents a selector switch, C| represents a connector switch, T3 represents apparatus associated with a trunk 65 leading to a toll operators position, and CD2 represents a cord at the toll operators position.

Each of the stations A, B, C and D is of the type usually employed in automatic telephone systems and includes a dial or other impulse sender for use in securing connections with other stations in the system.

The line-finder switches LFI and LFZ, the selector-connector switch SC, the selector switch SI, and the connector switch CI are all of the well-known Strowgertype. For a complete description of the structure of a Strowger type switch and the operation of a system employing III of the second edition of Automatic Telephony, by Smith and Campbell, published in 1921. For a description of the operation of a Strowger type switch when used as a line iinder, reference may be had to Patent No. 1,799,654 granted to R. L. Stokely April '7, 1931. For a dee scription of the operation of a Strowger type switch when used as a selector-connector in a branch exchange reference may be had to Patent No. 1,675,886 granted to A. E. Hague July 3, 1928.

The out-going trunk apparatus TI associated with trunk 50 comprises a line relay 3|, release relay 32, supervisory relay 33, auxiliary supervisory relay 34, cut-through relay 35, holding relay 36, transfer relay 38, and the three-element cold-cathode tube 39. `The control elementl of tube 39 is permanently connected to the tip conductor of trunk 50, the tube being adapted to be operatively responsive only to the connection of a high positive potential tol this conductor which condition results if the connection is extended to a toll operators position. 'Ihe break-down o-f the tube 39 causes the operation of transfer relay 38 thereby transferring the connection from trunk 50 to trunk 4|] leading to the attendants position.

The apparatus T2 associated with the trunk 49 leading to the attendants position comprises a line relay 4|, release. relay 42, lamp 43, cut-off relay 44 and answering jack 45.

The trunk apparatus T3, associated with the trunk 65 which terminates at a toll operators position, comprises a line relay 1|, release relay 12, auxiliary line relay 13, lamp 14, cut-off relay 8|) and answering jack 8|. To serve notice that the trunk T3 is a toll trunk, the tip conductor is normally connected to a high positive potential such switches reference may be had to Chapter branch exchange, the line-iinder switch LFI (or a, similar switch) is operated to ind and connect the calling line to a selector-connector switch such as SC which has access both to branch office lines and to trunks leading to the central oflice. If the number of lines in the vided, instead of selector-connector switches, for use in completing calls between stations in the branch ofice; and in this case, the trunks to the main oflice would be connected to terminals in the banks of the selector switches. The selector-connector SC is operated in response to dial impulses created by the dialing of therst digit of the number of the `called station to select a corresponding group of terminals, and, if the called station is inthe branch office, is thereupon operated in response to'dial impulses created by the dialingof the second digit of the number of the-called station to select the set of terminals to which the called station is connected. If the called station is in or beyond the main oiiice, the selector-connector isfoperated in response to dial -impulses created by the dialing of the first digit of the number of the called station to select a, group of terminals connected to trunks leading to the main office and to seize an idle trunk in this group. -Y

Assuming the calling line I to have been extended through brushes and I2 of line-nder switch LFI and brushes 2| andV 22 of selectorconnector switch SC to conductors 21 and 28 of trunk apparatus TI, the line relay 3| operates. Relay 3| closes a circuit for operating release relay 32; and relay 32 connects ground to sleeve conductor 29 to hold the selector-connector and line-finder switches and to hold the cut-01T relay (not shown) of-line I0 all in well-known manner. The operation of relay 3| disconnects the winding of holding relay 36 from the upper conductor of trunk 50, and-connects ground at the back contact of relay 34, through resistance 31, the inner left front contact ofY relay 3|, winding of supervisory relay 33 and` uppermost back contact of relay 38 tothe upperrconductor of trunk 5D. Since the line relay associated with trunk -50 in the mainV oilice, is connected only to the lower conductor of trunk 50, this connection of groundto theupper conductor of trunk 50 is without-effect. Relay 3| also closes a circuit from ground at the ba-ck contact of relay 34, through resistance 31, the right front Contact of vrelay 3|,. inner upper back contact of relay 38, over the lower conductor of trunk 58 to the main oflice, through the back Contact of cut-off relay 52 and the winding ofv line relay 5| to battery. Relayv 5| is Ythereby operated to cause an idle line-finder, which is assumed to be finder LF2, to hunt for and seize the terminals to which the conductors o`f trunk 50 are connected, in Well-known manner. YThe cut-off relay 52 is operated when the line is found and the conductors of trunk 59 are connected in usual manner to the windings of the line relay (not shown) of the first selector switch SI. A circuit is thereupon completed from battery through one winding` of the line relay of selector SI through brush 54 and terminal of line-nder LF2, over the lower conductor of trunk 5D, inner upper back contact of relay 38, right front contact and inner left front contact of relay 3|, Winding of relay 33, uppermost back contact of relay 38, upper conductor of trunk 5D, terminal and brush 53 of line-finder LF2, and through another Winding of the line relay of selector SI to ground. Resistance 31 is high enough so that relay 33 is suiciently energized to cause its operation. Relay 33 closes a circuit for operating the slow-to-release relay 34 thereby disconnecting the conductors of trunk T from ground at Y the back contact of relay 34. The operation of branch oflice were large enough both selector'- switches and connector switches would be'prothe line relay of the selector SI in the circuit over trunk 50 causes the connection of a holding ground potential Vto the sleeve conductor of the line-lnder LF2 in usual manner to hold the linefinder in operated position and to hold the cutoi relay 52. Y

The aforementioned operation of relay 34 also closes a circuit for operating relay 35. Relay 35 disconnects the line relay 3| and extends the oonnection from'line I0, over conductors 21 and 28, through-the uppermost and inner upper front contacts of relay 35, and through the upper back contacts of relay 38 over the conductors of trunk 50, through brushes 53 and 54 of line nder LF! to the windings of the line relay (not shown) of selector switch SI. The operation of relay 35 causes the release of relay 3| but holds relay 32. Resistance 30 is connected in parallel with the winding of relay 33 and in series with conductor 21 but relay 33 remains operated. Dial tone is transmitted from selector SI to the calling station inusual manner and in response to the impulses created by the dialing of the next digit the se.- lector SI is operated to select a corresponding group of terminals and to select and seize an idle set of terminals in this group. Since relay 34 is slow in releasing, the response of relay 33 to dial impulses does not cause the release of the connection. If the call is for a subscribers station D in the main oflice, the call is completed in response to the dialing of the remaining digits of the called subscribers number by the operation of intermediate selectors, if any, and a connector switch CI. Relay 38 of trunk apparatus TI remains normal since no potential high enough to break down tube 39 is connected to the tip conductor of trunk 50 on such a call.

If in response to the dialing of the second digit, the switch SI selects a trunk 65 leading to a toll operators position, the lower conductor of trunk 5I) is connected through brushes 54 and 62 of switches LF2 and SI, the uppermost back contact of relay 83, resistance 19 and the right winding of relay'1l to battery; and the upper conductor of trunk 59 is connected through brushes 53 and 6| of switches LFZ and SI, the inner back contact of relay 80, left winding of relay 1|, and through the backA contact of relay 13 to boosterbattery 15. Relay 1| is thereby operated and relay 33 held operated by the current over trunk 5U. Relay 1| closes a circuit for operating relay 13 and relay 13 connects ground potential to the left winding of relay 1| in place of the booster battery 15. During the short interval of time that booster battery potential remains connected to the upper conductor of trunk 50 after seizure of trunk B5, a current is started across the gap between elements b and c of tube 39 of trunk apparatus TI. The ionization of the gas in tube 39 by this current reduces the resistance between elements a and c so as to cause the operation of relay 38 by a current through its Winding, across elements a and c, over the upper conductor of trunk 56 to the booster-battery in trunk apparatus T3; Relay 38 operates andlock's through its lower front contact to holding ground potential at the front contact of relay 32. The disconnection of the booster battery potential by the operation of relay 13 'causes the deenergization of tube 39. The aforementioned operation of relay 1l also` closes a circuit for operatingthe slow-to release relay 12 which connects holding ground potential toJconductor69 tohold the line nder and selector Switches LFZ and SI and to hold the cut-offrelay 52. The aforementioned operation of `relay 13 also closes a circuit' for lighting the answering lamp 14. Due to the operation of relay 38 of. apparatus TI, the bridge across Athe conductors of trunk is opened and relay 1I releases. The release of relay 1| causes the release of relays 12 and 13 and the lamp 14 is thereby immediately extinguished to prevent the answer of the call by a toll operator. The release of relay 12 disconnects the holding ground potential from conductor 69 thereby releasing the cutoi relay 52 and causing the return of switches LF2 and SI to normal in usual manner.

The aforementioned operation of relay 38 extends the connection from the calling line over trunk 40 to trunk apparatus T2 at an intercepting operators position, the line relay 4| being operated by current through its windings in series with the line IU. Relay 4l closes a circuit for lighting the answering lamp 43 and a circuit for operating the slow-to-release relay 42.

When the intercepting operator answers the call by inserting the plug 41 of a cord CDI in the answering jack 45, relay 44 operates cutting off line relay 4I and closing a holding circuit for relay 42. The release of relay 4I extinguishes lamp 43. Since relay 42 connects. holding ground potential to conductor 29, theI connection is now held under the joint control of the operator and subscriber. The operation of key 49 completes a talking connection between the calling station and the operators telephone set.

When the plug 41 is withdrawn from jack 45, relays 44 and 42 release; and, when the receiver is replaced at station A, relays 33, 34, 35, and 32 release. With both of relays 32 and 42 released, the holding ground potential is disconnected from conductor 29, the switches LFI and SC being restored to normal in usual manner.

If the trunk 65 is selected by switch Sl on a call originated at a subscribers station C in the main oince, the temporary connection of booster battery 15 thro-ugh the left winding of relay 1| to the calling line is without effect. The operation of relay 1I in series with the calling line, causes the operation of relays 12 and 13. Relay 12 connects holding ground potential to conductor 69 and relay 13 lights the answering lamp 14. Relay 13 also short-circuits resistance 19 and connects the ringing generator 16 through condenser 11 to one of the conductors of trunk 65 to transmit a ringing tone to the calling station.

When the toll operator answers the call by inserting the plug 82 of a cord CD2 in jack 8l, relay 88 of apparatus T3 operates in series with a relay 83 of the cord. Relay 80 cuts off the line relay 1l andcloses a circuit for holding relay 12. Relay 83 completes a connection from the calling line over the conductors of trunk 65, jack 8| and plug 82 to the windings of repeating coil 84. Operation of the key 85 completes a talking connection between the calling subscriber and the toll operator.

Upon removal of plug 82 from jack 8l, relay 80 releases and, if the calling subscriber has replaced the receiver, relay 1I cannot reoperate. The release of relay 12 disconnects holding ground potential from conductor 69, the line finder and selector switches LFZ and Sl being restored to normal in usual manner.

The arrangement might be modified or incorporated in a system in which the trunk B5 is connected to terminals of intermediate selectors instead of to terminals in the banks ofV rst selectors as shown. In such a case the dialing of more than one digit would be required to select a trunk in the group which includes the trunk 65. The invention may, of course, also be applied to systems in which toll calls are automatically completed. In such a system the trunks employed in extending calls outside of the local zone would be provided with a booster battery connection as is the trunk apparatus T3 by which the completion of the connection would be prevented and a call from a branch oilice be diverted to an intercepting operators position.

What is claimed is:

1. In a telephone system comprising a branch exchange and an automatic main exchange and subscribers lines in each of said exchanges, an attendants equipment at said branch exchange, a trunk between said branch and main exchanges, another trunk for use in completing a toll call, signal responsive means individual to said rst mentioned trunk for transferring a call originating in said branch oce from said trunk to said attendants equipment, and means associated with said other trunk and momentarily operable in response to seizure of said other trunk for transmitting a signal to operate said signal responsive means.

2. In a telephone system comprising a branch exchange and an automatic central exchange and subscribers lines in each of said exchanges, an attendants equipment at said branch exchange, a trunk between said exchanges, and means comprising a three-element gas-lled tube associated with said Ytrunk for transferring a call originating in said branch exchange from said trunk to said attendants equipment.

3. In a telephone system comprising a branch exchange and an automatic central exchange and subscribers lines in each of said exchanges, an attendants equipment at said branch exchange, a trunk between said exchanges, another trunk for use in completing a toll call, means comprising a three-element gas-lled tube associated with said l'irst mentioned trunk for transferring a call originating in said branch exchange from said rst mentioned trunk to said attendants equipment, and means associated with, and operable responsive to the seizure of, said other trunk for momentarily connecting to said trunk a potential high enough to cause the operation of said gas-nlled tube.

4. In an automatic telephone system, a branch cnice, a main office, subscribers lines in each of said oices, a trunk for use in connecting a calling line in said branch oice to said main ofce, a toll operators position, a trunk extending from said main ofce to said position, a high potential source of current normally connected to a conductor of said toll trunk, switching means for seizing said toll trunk and connecting a calling line in saidmain oilce or said trunk from the branch ofiice to said toll trunk, and means operatively responsive to seizure of the toll trunk for disconnecting said high potential source.

5. In a telephone system comprising a branch exchange and an automatic main exchange and subscribers lines in each of said exchanges, an

attendants equipment at said branch exchange, a vtrunk between said branch and main exchanges, another trunk for use in completing a toll call, signal responsive means individual t0 Y said first-mentioned trunk for transferring a necting a calling line over said trunk to said central exchange, a trunk outgoing from said central exchange for use in completing calls originating in either of said exchanges, subscriber con trolled switching means for use in connecting either a calling line in said central exchange or the first-mentioned trunk to the second-mentioned trunk, an intercepting operators position, means comprising a switching relay for transferring a calling line in said branch exchange from connection with said rst trunk to said intercepting operators position, and signaling means immediately effective upon interconnection of said first and second trunks for operating said switching relay.

RAY L. STOKELY; 

